Final answer:
In flea allergic dermatitis (FAD), a Type I hypersensitivity response is characterized by immediate, IgE-mediated reactions upon re-exposure to an allergen. Over time, this response can become more significant. Delayed hypersensitivity, on the other hand, involves a slower, cell-mediated response notable in skin reactions to certain substances like jewelry or cosmetics.
Step-by-step explanation:
Type I Hypersensitivity and Flea Allergic Dermatitis (FAD)
When discussing flea allergic dermatitis (FAD), we are focusing on a Type I hypersensitivity response that becomes more pronounced over time. In Type I hypersensitivity, an affected individual, once sensitized to an allergen such as flea saliva, will have a rapid immune response almost immediately upon re-exposure. This response is mediated by IgE antibodies which sensitize mast cells, leading to inflammation and allergy symptoms. Over time, the allergic response can become more severe as the individual's immune system becomes increasingly sensitized to the allergen.
Delayed Hypersensitivity
In contrast, delayed hypersensitivity involves a cell-mediated response that typically takes one to two days to manifest after the second exposure to an antigen. This response is T-cell mediated and contributes to conditions like contact dermatitis, which is evident in reactions to substances like certain jewelry or cosmetics. Delayed hypersensitivity also plays a role in the immune response to poison ivy and the tuberculin skin test for tuberculosis, where a previous exposure leads to a noticeable inflammation.